As generally known, a seat reclining apparatus for a vehicle seat that includes a seat cushion and a seat back inclinable relative to the seat cushion, has an operation range of the seat back. The operation range includes a reclining range in which the seat back can be stepwise inclined and locked in an inclining position, and a so-called free range in which the seat back is inclinable and free from being locked. In a typical seat reclining apparatus, the reclining range is defined between a substantially upright position and a rearwardmost inclining position (so-called full-flat position), and the free range is defined between the substantially upright position and a forwardmost inclining position, so that the operation range defined between the forwardmost inclining position and the rearwardmost inclining position is set as a sum of the reclining range and the free range which is substantially 180 degrees.
There have been provided various kinds of structures for a so-called recliner formed with a generally disk-shaped unit of an articulated portion or a hinged portion through which the seat cushion and the seat back are connected with each other to thereby serve adjustment of an inclining position of the seat back relative to the seat cushion. For instance, Patent Literature 1 discloses a seat reclining apparatus with a recliner that includes a base member, a cover member facing the base member, and three tooth plates disposed therebetween. In a reclining range of the seat reclining apparatus, the tooth plates are positively disengaged from and engaged with an internal tooth gear of the cover member, thereby changing an inclining position (attitude) of the seat back relative to the seat cushion and locking the seat back in the inclining position. On the other hand, in a free range of the seat reclining apparatus, the respective tooth plates is restrained to be in an unlock state in which the tooth plates are kept disengaged from the internal tooth gear of the cover member, thereby changing the inclining position of the seat back without being locked in the inclining position. Further, arcuate guide portions are formed on both the internal tooth gear and the cover member so as to restrain movement of the respective tooth plates in the free range.
In such a recliner of the above conventional art, as the number of tooth plates are increased, it becomes important to avoid overlap of the reclining range and the free range. In order to avoid the overlap, in the seat reclining apparatus of the above conventional art, the guide portions are changed in position (thickness) from each other in an axial direction of the cover member.